[weakrefs] Clear unregister token-related fields when clearing weak cells

Bug: chromium:1213770
Change-Id: Ic063e79bfa8f3dabdd29d1cc9ed74c7af44d0c31
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2923294


Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Shu-yu Guo <syg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74890}